Mobile communication terminals, also known as cellular phones, mobile phones or personal digital assistants, have been in ever increasing use for several decades now. In recent years, the most popular type of mobile communication terminal is the one which has a touch-sensitive display screen, or shortly a touch display, as the main input/output device for interaction with the user. Smartphones and tablets are the two dominating device types of this kind. A smartphone with a touch display will therefore be used as a non-limiting example of a mobile communication terminal throughout this document.
The present inventors have identified a problem with smartphones, which has to do with their inherently mobile nature in combination with their inherent susceptibility to accidental actuation by unintentional contact with the touch display. If a smartphone is accidentally actuated in this way, an unwanted function may be performed in and by the smartphone.
Measures have been taken in existing smartphones to prevent such accidental actuation. The prevailing approach is to have a special mode in which the user is generally prevented from accessing the functionality which is offered by the mobile communication terminal in its normal operational mode. The special mode is referred to as a lock screen mode in this document, and the appearance of the touch display in the lock screen mode is referred to as the lock screen.
The lock screen mode is not an idle mode; the touch display is kept turned on at the same screen brightness as in normal operational mode, or at least at a reduced screen brightness with some display visibility remaining. Moreover, certain limited functionality is typically available to the user in the lock screen mode. Such limited functionality typically includes presentation of status icons and information about the current time and date. The limited functionality typically also includes some contents or controls which the user may interact with, such as a message notification control, a missed call notification, an emergency service call control or a camera control. Hence, the user may interact with the services associated with these controls directly from the lock screen.
The lock screen mode can be entered in several different ways. A first way is by a user command from the normal operational mode. A second way is after expiry of an idle timer in the normal operational mode. A third way is by pressing an actuator on the smartphone while in inactive mode. An inactive mode, or idle mode, is a mode essentially without user interaction ability and serves to save power. The touch display is turned off and is not sensitive to touch in the inactive mode. For instance, pressing the power button or the home key on many smartphone models will cause entry into the lock screen mode from the inactive mode.
To exit the lock screen mode and switch to the normal operational mode usually requires some sort of unlock command from the user. A very common type of unlock command is a swipe motion, or slide motion, in a given direction on the lock screen. In some smartphone models, any direction will do. Another common type of unlock command is a passcode enterable by a sequence of taps on digits or characters on a virtual keypad on the lock screen.
The problem that the present inventors have identified is, more specifically, that situations occur more or less frequently where users accidentally enter the lock screen mode from the inactive mode by pressing the relevant actuator (e.g. power button or home button). One usual situation is when the user intends to put away the smartphone and actuates the actuator unintentionally. The situation is particularly common when the smartphone is put in a pocket, briefcase, jogging holder or similar narrow storage space, since the user will have to hold the smartphone in a certain finger grip in order to fit the smartphone into the pocket, etc., and may then reach contact with the actuator inadvertently.
Since the unintentional switch to lock screen occurs when the smartphone is put away, the user will often not notice that the touch display is turned on. As a result, the touch display will be susceptive of touch actuation without the user knowing it, and accidental actuation by contact between the leg or arm of the user and the touch display may take place.
Such accidental actuation may for instance cause a spurious swipe motion on the touch display when the terminal is put into a pocket. Therefore, accidental actuation is not always prevented even if the smartphone's unlock command involves a swipe or slide motion—and likewise for other controls on the lock screen.
If the unlock command is a passcode, repeated accidental actuation may cause repeated spurious taps on digits or characters on the virtual keypad, and hence result in an incorrect passcode being entered repeatedly, whereupon the smartphone will be blocked from further use.
The problem above is accentuated by the diversity of mobile communication terminal users. Nowadays, users of mobile communication terminals are a very heterogeneous group in which there are considerable variations in terms of age, user experience, physiological motor ability, visual capacity, and general user preference.
Particularly for inexperienced or otherwise impaired users, it is desired to improve the prevention against accidental lock screen commands in terms of reliability and user-friendliness.